Known tire inflation systems, for example that of U.S. Pat. No 4,434,833, have a contact seal at the interface between the rotating and non-rotating passages in order to ensure there is no leakage of pressurized air. However, whenever the vehicle is moving, the seal is in permanent rotating rubbing contact with an adjacent component. This permanent rubbing causes contact friction which in turn results in power loss, as well as uneven wear of the seals which results in deterioration of the seal and its effectiveness.
U.S. Pat. No. 4,705,090 discloses a prior art tire inflation system which attempts to overcome this problem by providing a sealing arrangement between the rotating and non-rotating passages that includes a displaceable seal on the non-rotating component that is normally maintained out of contact with the rotating component. In this system, the displaceable seal can be moved into engagement with the rotating component by air under pressure from a first air line. This system, however, requires the provision of a second air line for the supply of air to a vehicle tire once the seal is in the engaged position. Significantly, air from the first air line is not supplied to the vehicle tire.
U.S. Pat. No. 4,892,128 describes a less complex tire inflation system with a single air line which has seals between the rotating and non-rotating components that are lightly engaged in normal use. When it is desired to change the tire pressure, air within the pressure control system is used to bring the seal members into heavy engagement, air from the same line then being supplied to the tire. Whilst this actuation system is simpler than that of U.S. Pat. No. 4,705,090, it suffers the aforementioned disadvantage of permanent contact friction between the seals, subsequent deterioration of the seals and power loss.